Certain processing schemes and architecture are disclosed in Patent Cooperation Treaty Application No: PCT/US2008/002058, entitled, SOLAR CELL WITH TEXTURED SURFACES, Filed: Feb. 15, 2008, in the names of Emanuel M. Sachs and James F. Bredt and The Massachusetts Institute of Technology, designating the United States of America, the National Phase of which is U.S. patent application Ser. No. 12/526,439, issued as U.S. Pat. No. 8,257,998 on Sep. 4, 2012, and also claiming priority to two provisional United States applications, No. U.S. 60/901,511, filed Feb. 15, 2007, and No. U.S. 61/011,933, filed Jan. 23, 2008. All of the PCT application, the U.S. patent, patent application, and the two US provisional applications are hereby incorporated fully herein by reference. The technology disclosed in these applications is referred to herein collectively as Self Aligned Cell (SAC) technology.
Certain additional processing methods and apparatus are disclosed in Patent Cooperation Treaty Application No. PCT/US2009/002423, entitled WEDGE IMPRINT PATTERNING OF IRREGULAR SURFACE, filed Apr. 17, 2009, in the names of Benjamin F. Polito, Holly G. Gates and Emanuel M. Sachs, and the Massachusetts Institute of Technology and 1366 Industries Inc., designating the United States of America, the National Phase of which is U.S. patent application Ser. No. 12/937,810, and also claiming priority to two provisional United States applications, No. U.S. 61/124,608, filed Apr. 18, 2008, and No. U.S. 61/201,595, filed Dec. 12, 2008. All of the PCT application, the U.S. patent application, and the two US provisional applications are hereby incorporated fully herein by reference. The technology disclosed in the applications mentioned in this paragraph is referred to herein collectively as wedge imprint technology or wedging technology, although in some instances protrusions having shapes other than wedges may be used. The related applications are referred to below as the Wedging applications.
In brief, such wedge imprint technology includes methods. Patterned substrates with a specified texture for photovoltaic and other uses are made. As shown with reference to FIGS. 1, 2, 3, 4, and 5 and 6 of the Wedging Application, the substrates are made by impressing protrusions of a flexible stamp, upon a thin layer of resist material, which covers a substrate wafer. The stamp tool used is of a material (typically elastomeric) that is soft enough so that the tool deforms upon contact with the substrate or wafer upon which a coating of resist has been previously applied. The resist becomes soft upon heating and moves away from the locations of impression at the protrusions under conditions of heat and pressure, revealing regions of the substrate adjacent to the protrusion. (The resist can be heated before or after the protrusions contact the resist or both before and after, as well as during.) The substrate is then cooled with the stamp in place, and the stamp is removed, leaving regions of the substrate exposed under holes, from where the resist has been moved away. The substrate can be further subjected to some shaping process, typically an etching process. Exposed portions of the substrate are removed by an action, such as etching, and portions of the substrate that are protected by the resist, remain.
A typical substrate is silicon, and a typical resist is a wax or a mixture of waxes, resins and rosins. The stamp may be used over and over again. The protrusions of the stamp may be discrete, spaced apart, such as the pyramidal elements shown. Or, they may be extended, wedge shaped elements, such as shown in the wedging applications. Or, they may be a combination thereof, or any other suitable shape that can cause the resist material to move away from the original covering condition.
Thus, a stamp is used to pattern a resist layer on a workpiece, which is then subjected to a different shaping step, to shape the workpiece. The workpiece may then be used for photovoltaic, or other uses. Textures that can be provided to the workpiece include extended grooves, discrete, spaced apart pits, and combinations thereof, as well as intermediates thereof. Platen based techniques may be used for patterning the workpiece. Rough and irregular workpiece substrates may be accommodated by using extended stamp elements to insure that the shaped portion of the stamp contacts the surface of the workpiece. Methods described in the wedging application and above are referred to herein as wedge imprinting or wedging.
Thus it is often desirable to coat very thin films of polymers onto substrates. A particular set of applications discussed above is in the area of defining patterns, for example, in a polymeric resist, which then acts to block etching. A thinner film is helpful in defining smaller features. For example, for features of 2-5 microns, a film of less than 5 microns thick and typically less than 3 microns is desirable. Typically such thin polymer films are deposited as a polymer dissolved in an organic solvent or finely dispersed in a carrier liquid. A film of thickness greater than the desired polymer thickness is deposited and this film thins down to the desired thickness as the solvent or carrier fluid evaporates.
However, using solvents places a burden on the environment. Using solvent requires more expensive equipment within the factory: to provide a safe breathing environment for workers, to avoid and suppress fires, and to remove solvent from exhaust streams entering the external environment. Inherent in using a solvent or dispersion is the addition of a process step to dry the coating down to its final thickness, which adds complexity and cost to the process. Shipping cost is increased when using liquid materials with bulk far in excess of the functional polymer content, and shipping of hazardous solvents involves additional cost. Finally, the shelf-life of polymers dissolved in solvents or carried in a dispersion is often limited, thus causing logistical problems and waste.
Thus, it can be desirable to deposit a thin polymer film without using a solvent or carrier fluid. There is need for such a process and for apparatus to carry out such a process. These, and other objects of invention hereof will be readily understood with reference to the Figures of the Drawing, which are: